The invention relates to the manufacture of particle board, hardboard, and laminated wood products and particularly to the continuous manufacture of such products utilizing an endless belt structure.
The conventional method of manufacturing particle board utilizes wood residues, fibers from wood chips, or similar wood products, mixes them with a resin or glue, places the mix in a stationary hydraulic press, compresses the material between two fixed platens to a desired thickness, and then heats the platens by applying steam through conduits therein. The application of heat for a given amount of time sets the resin. The platens thereafter are released and the board is trimmed to a desired size. The apparatus necessary to perform the above process requires an extremely large investment, not only in terms of the required machinery, but also in terms of the physical size of the manufacturing facility.
Furthermore, the conventional process has a disadvantage in that there is a substantial time element involved in the curing process, and the machine is effectively tied up for the curing period preventing the set-up of the next cycle of operation. It obviously is more desirable to employ a continuous process wherein the particle board material is compressed, cured and delivered from an apparatus without the necessity of changing the machine configuration to perform these operations.
A process for continuous particle board manufacture also may be adapted to the manufacture of laminated plywood, wall paneling or the like. While the general thrust of the present disclosure is directed to particle board manufacture on a continuous basis, it should be understood that the system disclosed is readily adaptable to a number of manufacturing processes for board or like materials.
There are at least two continuous particle board manufacturing devices presently available. One of these utilizes two caterpillar track systems facing each other for feeding a mat into the machine at one end, compressing the mat therebetween into a board to a desired thickness, and then ejecting the cured board. However, as the machine wears, a problem faced is that there is deflection as the board material is passed through the machine. A formed board may result which has irregular surfaces because of this. Such a method of manufacture may require the boards to be sanded and finished after they are ejected from the machine. Such a step obviously lessens the efficiency of the method and associated apparatus. Additionally, the apparatus necessary to perform the various functions, especially the caterpillar-like tracks, requires the use of an enormous amount of steel. This is necessary, in order to limit, as much as possible, the deflection of the tracks due to the high working pressures required to compress the mat. It is also necessary to introduce heat into the track system, which is quite costly and complicated, for the purpose of curing the board. The heat loss through the mass of metal is great as is the heat required to bring the press up to the required temperature.
A second device for manufacturing board material on a continuous basis utilizes a drum which rides against a steel belt such that the material is fed between the belt and the drum. The material is heated by steam or other known heating systems as the drum rotates. The material is squeezed between the drum and belt to a desired thickness and is ejected at an output end in a fairly rigid form. The problem with this apparatus is that the drum limits the thickness of the boards obtainable by this process. For example, it has been almost impossible to deliver boards thicker than three-eighths of an inch by this process, because of the required bending of the board between the belt and drum. Unless the board is thin enough to bend around the periphery of the drum, the finished board will be destroyed before it can be ejected from the machine.
Curing is another problem faced in manufacturing particle board. One method of curing the board is by steam, but during application of steam heat to the boards, the outer surfaces of the boards are cure hardened by conductivity through contact with the heated platens and the like. Moisture trapped between the outer surfaces of the board has a tendency to form steam pockets under the surface of the board. When the pressure is released, the steam becomes rapidly unrestrained, causing a blowout of the particle board surface, thereby destroying the product and establishing a considerable waste factor.
Another method of curing is by the use of dielectric heating. However, the apparatus employed generally utilizes the stray field concept, which involves electrodes at spaced intervals generating a field which crosses through the mat to be cured. This method, while operable, has proved somewhat inefficient in application because, firstly, it is basically a preheater and not available during the final cure, and, secondly, the R.F. field produced at the electrodes must cross through the metal platens, thus absorbing some of the energy generated.
It is, therefore, an object of the present invention to provide an apparatus which obviates one or more of the limitations and disadvantages of the described prior arrangements.
It is another object of the present invention to provide a system which produces a particle board of any reasonable desired thickness on a continuous basis.
It is another object of the present invention to provide a system for the efficient continuous curing of a particle board under manufacture.
It is yet another object of the present invention to provide a simplified and inexpensive method of producing boards adaptable to such manufacture on a continuous basis.